Mechanical torques are applied to dorsiflex or plantarflex the ankle of a normal, human subject, seated in a relaxed position. The angular rotation of the foot and electromyographic responses from the lex flexors and extensors are recorded by a computer for later analysis. These data are analyzed to develop quantitative relationships between the mechanical input and the subject's response and the dependence of these relationships upon voluntary actions at the time of the stimulus and subsequent to it as determined by prior instruction.